The invention relates to a system for determining a position of a moving transponder.
Many areas of sports require determination of position and/or time of the participants, including car racing, athletics and skating. To achieve such a determination the participants carry a transponder being in communicative connection with measuring stations.
FR 2 619 644 discloses a detection system for detecting the time of cars in a car racing event. The cars each have a transponder emitting signals that are received by a receiving unit. The transponders receive magnetic field signals from an antenna loop in the track. The receiving unit determines the time of passing of the cars by manipulating the received signal, which has a frequency in the range of 2-3 MHz.
The prior art system is problematic in that the transmitted magnetic signals only have a small bandwidth, since magnetic coupling requires a relatively low carrier frequency. Such a relatively small bandwidth puts restrictions on the number of transponders that can be employed in a sporting event. Moreover limitations exist as to the distance for detection of the signal of the transponder since the power of these magnetically transmitted signals decreases rapidly with the distance to the antenna.
However, employing an electromagnetic transmission method is problematic as well. The unit receiving such electromagnetic signals will often not be able to determine a position of the transponder, since these electromagnetic signals show a highly irregular pattern, mainly as a result of multi-path effects associated with electromagnetic signals of relatively high frequency.
It is therefore desirable to provide a system employing a high bandwidth while still being able to determine the position and/or passing time of a transponder.